On Friday we'll be updating Chicken Invaders 4 to bring it up to date with the latest changes from Chicken Invaders 5. We've taken great care to upgrade your existing career, stats, achievements, keys, leaderboards, and local high scores.
However, your in-mission progress will NOT be upgraded. To avoid losing any progress, either finish your current mission by Friday, or set the game to update only on launch and keep Steam in offline mode until your mission is complete.
This is due to technical restrictions which unfortunately cannot be avoided. We'll do our best so that mission progress is preserved in future updates. Thanks for your understanding!